An exhaust gas sensor may be positioned in an exhaust system of a vehicle to detect an air/fuel ratio of exhaust gas exhausted from an internal combustion engine of the vehicle. The exhaust gas sensor readings may be used to control operation of the internal combustion engine to propel the vehicle.
Degradation of an exhaust gas sensor may cause engine control degradation that may result in increased emissions and/or reduced vehicle drivability. Accordingly, accurate determination of exhaust gas sensor degradation may reduce the likelihood of engine control based on readings from a degraded exhaust gas senor. In particular, an exhaust gas sensor may exhibit six discrete types of degradation behavior. The degradation behavior types may be categorized as asymmetric type degradation (e.g., rich-to-lean asymmetric delay, lean-to-rich asymmetric delay, rich-to-lean asymmetric slow response, lean-to-rich asymmetric slow response) that affects only lean-to-rich or rich-to-lean exhaust gas sensor response rates, or symmetric type degradation (e.g., symmetric delay, symmetric slow response) that affects both lean-to-rich and rich-to-lean exhaust gas sensor response rates. The delay type degradation behaviors may be associated with the initial reaction of the exhaust gas sensor to a change in exhaust gas composition and the slow response type degradation behaviors may be associated with a duration after an initial exhaust gas sensor response to transition from a rich-to-lean or lean-to-rich exhaust gas sensor output.
Previous approaches to monitoring exhaust gas sensor degradation, particularly identifying one or more of the six degradation behaviors, have relied on intrusive data collection. That is, an engine may be purposely operated with one or more rich to lean or lean to rich transitions to monitor exhaust gas sensor response. However, these excursions may be restricted to particular operating conditions that do not occur frequently enough to accurately monitor the sensor, such as during deceleration fuel shut off conditions. Further, these excursions may increase engine operation at non-desired air/fuel ratios that result in increased fuel consumption and/or increased emissions.
The inventors herein have recognized the above issues and identified a non-intrusive approach for determining exhaust gas sensor degradation. In one embodiment, a method of monitoring an exhaust gas sensor coupled in an engine exhaust comprises indicating exhaust gas sensor degradation based on a difference between a first set of estimated parameters of a rich operation model and a second set of estimated parameters of a lean operation model, the estimated parameters based on commanded lambda and determined lambda values collected during selected operating conditions.
In this way, exhaust gas sensor degradation may be indicated by parameters estimated from two operation models, a rich combustion model and a lean combustion model. Commanded air-fuel ratio and the air-fuel ratio indicated by the exhaust gas sensor may be compared with the assumption that the combustion that generated the air-fuel ratio was rich (e.g., inputting the commanded lambda into the rich model) and also compared assuming that the combustion event was lean (e.g., inputting the commanded lambda into the lean model). For each model, a set of parameters may be estimated that best fits the commanded lambda values with the measured lambda values. The model parameters may include a time constant, time delay, and static gain of the model. The estimated parameters from each model may be compared to each other, and sensor degradation may be indicated based on differences between the estimated parameters.
By determining degradation of an exhaust gas sensor using a non-intrusive approach with data collected during selected operating conditions, exhaust gas sensor degradation monitoring may be performed in a simple manner. Further, by using the exhaust gas sensor output to determine which of the seven degradation behaviors the sensor exhibits, closed loop feedback control may be improved by tailoring engine control (e.g., fuel injection amount and/or timing) responsive to indication of the particular degradation behavior of the exhaust gas sensor to reduce the impact on vehicle drivability and/or emissions due to exhaust gas sensor degradation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.